Use the properties of the delta function to deduce its Fourier transform.
By definition
{\mathcal{F}}\{\delta(t-a)\}=\int_{-\infty}^{\infty}\delta(t-a)\,\mathrm{e}^{-\mathrm{j}\omega t}\,\mathrm{d}t
Next, recall the following property of the delta function
\int_{-\infty}^{\infty}f(t)\delta(t-a)\,\mathrm{d}t=f(a) (24.9)
for any reasonably well-behaved function f (t). Using Equation (24.9) with f (t ) = e^−{j \omega t} we have
{\mathcal{F}}\{\delta(t-a)\}=\int_{-\infty}^{\infty}\mathrm{e}^{-\mathrm{j}\omega t}\delta(t-a)\,\mathrm{d}t=\mathrm{e}^{-\mathrm{j}\omega t}In particular, if a = 0 we have {\mathcal{F}}\{\delta(t)\}=1. This result is depicted in Figure 24.9.